The present invention relates to a device for continuously inspecting surface conditions such as the surface smoothness of a belt-like article which is long and wide. More particularly, the invention relates to a device for quantitatively inspecting and measuring variations in the smoothness of the surface of a belt-like article such as a high-quality coated paper whose surface flatness must be accurately and precisely monitored so that the surface smoothness is maintained within an allowable range.
In general, a process of manufacturing high-quality coated papers or the like must be strictly controlled. However, in the course of manufacturing such articles, it is difficult to completely prevent defects from occurring such as the occurrence of defects in the form of projections which are due to relatively large particles contained in the surface coating material. Accordingly, it is essential to check for the occurrence of such defects at all times in order to be able to remove the defective articles.
In a conventional method for continuously inspecting the surface of an elongated article of the type described above, in general, foreign matter or projections are detected from the vertical movement of a roll provided on a lever arm which precisely follows the surface of the article. However, such a method utilizing a contact system is disadvantageous in the following points. The measurement accuracy varies greatly with the speed of an object or an article to be inspected. Secondly, whenever an object or an article to be inspected is different in thickness, an adjustment of the inspecting apparatus is quite troublesome. Furthermore, when foreign matter or a protrusion is detected, the article may be scratched. That is, secondary damage may be inflicted on the article and at worst the article may be deformed or torn.
On the other hand, a method of monitoring the surface of an article for unevenness and scratches has been employed which utilizes an optical system in which no roll is brought into contact with the object to be inspected. Such a system has been employed for inspecting, for instance, oil packages which are used for the brake system in an automobile. (See, for example, Japanese Laid-Open Patent Application No. 99360/1975.) If such an optical system is employed, the disadvantages accompanying the above-described method utilizing a contact system can be eliminated. However, such a system which is capable of operating with a belt-like article has been herebefore unknown.